For the application of thin carbon layers, different process variants of the basic process of physical and chemical vapor phase precipitation are used. For carbon layers on magnetic fixed disks, for which there are high requirements with regard to smooth surface and the avoidance of particles on the surface, only those procedures which use the principle of magnetron sputtering, i.e. by atomizing the target material in a vacuum, have been able to be carried out until now. In addition, the precipitation rate achieved through magnetron sputtering exceeds the values achieved using other precipitation procedures in a vacuum.
In using carbon layers applied using magnetron sputtering as protective and gliding layers for magnetic disk memories, the required layer characteristics, particularly hardness, abrasion resistance, tribological behavior, corrosion resistance and adhesion for additional lubricant layers to be applied, that is the layers applied subsequently, can be achieved by suitably selection of the hydrogen content of the carbon layers (H. J. Lee et al., Surface and Coatings Technology, 54/55(1992)552-556). Depending on the application, layers will contain, for example, 15 to 30 at percent of hydrogen. The manufacture of these layers therefore takes place in a reactive sputtering process in which the process gas is an argon-hydrogen mix or at least contains hydrogen or hydrocarbon. In this way, the specific electrical resistance of the carbon layers increases with an increase in the hydrogen content. In addition, the layer characteristics are also influenced by other parameters in the sputtering process, such as pressure of the process gas, temperature of the substrate, power density from the target and ion and plasma effects which, for example, can be set through direct voltage on the substrate (voltage distortion).
It is a known procedure to apply DC magnetron sputtering, i.e. to feed the magnetrons with direct current. The disadvantage of this procedure is that instabilities in the process occur with an increase in process time. These are apparent through an increasing tendency to form local arc discharges, called arcing. An effect of arcing can be seen in particles built into the layer and protruding above their surroundings, their size being a multiple of the thickness of the layer. With an increase in storage density and a reduction in the head height, i.e. the distance between the read/write head and the fixed disk, such particles have an increasingly critical effect on functionality. At a storage density of, for example, 1Gbit/inch.sup.2 and a head height of below 50 nm, it is understood that particles are generally not permitted, even if their size is clearly below 1 .mu.m.
The formation of arc discharges in reactive sputtering has been known for some time and all types of attempts have been made to prevent them as they lead to a reduction in the layer quality. It has been said that the cause is local areas of high current density on the cathode and a thermal electron emission in areas linked to these areas of high current density. The magnetron discharge reaction in an arc discharge is caused by the electrical discharge of insulating layers, particularly the insulating layers formed in the reactive sputtering process from reaction processes between the target material and the reactive gas. The disruptive electrical discharge of these charged target areas leads to reactions in an arc discharge. This is linked to a drastic fall in the operating voltage, an increase in the current and localization on one or more arc spots and consequently to the melting and splattering of target material. These so-called "catastrophic arcs" lead to the formation of numerous defects in the layer and to damage to the target surface, so that the damaged spot becomes the starting point for new arc discharges.
For the sputtering of carbon, the damaged spots occurring on the target, so-called "nodules" and their negative effects on the stability of the process is described in detail in U.S. Pat. No. 5,507,930.
It is known how to build power supplies for the magnetron so that when a "catastrophic arc" occurs, the energy feed is interrupted for a certain length of time. After switching on the power supply again, the sputtering process generally either continues or an arc discharge is recognized again and the power supply interrupted again. In order to limit the effects of "catastrophic arcs", the DC power supplies are equipped with fast-acting interruption devices, generally in combination with LC switching (DE 195 37 212).
It is additionally known that apart from the occurrence of "catastrophic arcs" which are greatly reduced, additional arc discharges of another type, so-called "microarcs" occur in the reactive sputtering of carbon. These differ from "catastrophic arcs" in that the amount of energy they contain is considerably less and falls in the range of 10 to 100 mWs. In addition, such "microarcs" extinguish themselves without the energy feed being reduced for any time. However, "microarcs" also lead to defects in the layer.
It is also known how to periodically pulse the energy feed for the magnetrons using a certain frequency of, for example, 1 to 100 KHz to prevent arc discharges (DE 41 27 317, DE 37 00 633, DE 41 36 665, DE 42 02 425, DE 41 27 504, DE 42 23 505). In addition to the pulse shaped energy feed, part of this solution also contains the short-circuiting of target and anode. The short-circuit is effected through fast breaker units and is triggered either periodically or after recognizing an arc discharge.
Finally, it is also known how to reduce the probability of arc discharge reactions by the magnetron discharge being fed through a DC voltage source with a sinusoidal alternating voltage superimposed on the DC voltage U.S. Pat. No. 5,507,930.
These known procedures have the disadvantage that in depositing hydrogenous carbon layers using reactive magnetron sputtering, even taking into consideration all the stated process variants, no process for long-term stability can be carried out which leads to low-particle layers. The particle density on the layers increases gradually after a processing time of several hours. The process must be interrupted and the sputtering installation must be ventilated. Numerous irregularities can be seen on the target, generally known as "nodules" or "black flowers". The coating process cannot be restarted until the target has been replaced or cleaned. The uninterrupted process time depends on the requirements in permitted particle density. For the storage density characterized at the start, the ratio between process time and regeneration time is already intolerably low. In addition, there is a high manufacturing risk in that the particle density cannot be determined until the subsequent quality controls. An in-situ quality control for particle density on the carbon layers and, thus, for the stability of the process is not known.